1. Move the cursor to the start of the text block you want to define.
2. Type M-space (the META character followed by a space).
This sets a 'mark' at the start of the 'region'.
3. Move the cursor to the end of the text block you want to define as the 'region'.
This sets the 'point' at the end of the 'region'. You do not have to type anything to set this 'point', the 'point' is the location of the cursor.